1. Field of the Invention
The present invention relates in general to a method and apparatus for controlling fluid flow using a check valve. More particularly, the invention relates to a self piloted check valve for controlling fluid flow in high vibration environments.
2. Description of the Related Art
Check valves are used in a wide variety of applications. Historically, conventional check valves are generally the least reliable type of valve. This is a consequence of flow for an open valve continually passing both the seat and the sealing plug or ball of those check valves. This problem can lead to very rapid valve failure, particularly in abrasive flow applications or when larger objects pass by the valve. Oilfield applications, particularly use in the drilling of wells, typically cause conventional poppet valves or flapper valves to leak in 15 hours or less of service. Such check valve applications are particularly critical, since they provide the first line of defense against well blowouts.
Another major problem for any check valve is survival in high vibration environments. Relative motion of components resulting from high vibrations can rapidly induce wear in the constituent valve components, particularly in abrasive environments, such as oilfield drilling muds or slurries. When a valve is used immediately above the bit in oilfield drilling, it is commonly termed a “float valve”. While all components in a drill string are subject to relatively high vibrations, float valves are exposed to very high vibratory accelerations of 10 times gravity or more while passing flows often in excess of 600 gallons per minute. Relative motion of adjacent parts in the abrasive drilling fluid environment can cause rapid wear sufficient to cause misalignment between the sealing member of a valve and its valve seat. The very high flow rates in drill strings also can cause severe flow induced vibrations in parts in the flow passage of the valve. Flow induced vibrations in abrasive environments can lead to rapid wear in both any exposed components and their supports.
The earlier self piloted check valve, covered by U.S. Pat. Nos. 4,220,176 and 4,254,836, performs exceptionally well in nonvibratory environments. While the check valve covered by these earlier patents is exceptionally durable and can in general operate without maintenance for much longer periods than other types of check valve, improvements to the existing design are needed in its resistance to vibration induced wear caused by vibrational relative motion between adjacent valve components induced by both drillstring motions and flow induced vibrations of parts in the flow passage of the valve.
A critical need exists for an improved check valve which has enhanced resistance to both flow induced and vibration induced wear.